Experimental Investigation of Nonlinear Coupling of Lower Hybrid Waves on Tore Supra

Goniche, M.; Frincu, B.; Petržı́lka, V.; Berger‐By, G.; Hillairet, J.; Litaudon, X.; Preynas, M.; Voyer, Damien

doi:10.13182/fst12-a14623

Cited by 4 publications

(6 citation statements)

References 20 publications

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“…The width of the first density layer is set to be 2 mm, as a result of the fact that the guard limiters protrude ∼2 mm from the front surface of the launcher, while the width of the second layer is assumed to be infinite. By comparing the experiments and the ALOHA predictions, it is found that the measured density by Langmuir probe is overestimated, similar to the previous observations in Tore Supra [25,26]. The reasons may be the steep gradient of the density in private region, ponderomotive forces depressing the density in a very thin layer near the antenna, and underestimate of the collecting area (non-planar probe).…”

Section: Coupling Characteristicssupporting

confidence: 77%

First experimental results of the PAM LHCD launcher at 2.45 GHz on EAST

Li¹,

Liu²,

Wang³

et al. 2023

Nucl. Fusion

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This paper presents the first results of a passive active multijunction (PAM) launcher at 2.45 GHz during the lower hybrid current drive (LHCD) experiments on EAST. Good coupling performance with a power reflection coefficient (RC) ~ 3% has been achieved at the plasma-antenna distance up to ~ 11 cm in L-mode edge plasmas without local gas puffing near the PAM launcher. Reliable power coupling of this PAM during the edge perturbations induced by type I ELMs has been successfully demonstrated. Compared with the old full active multijunction (FAM) launcher, the new PAM can be placed ~ 2 cm further away from the plasma in normal operations, which is in good agreement with the previous prediction (Li et al. 2019 Fusion Eng. Des. 147 111250), by the linear wave-plasma coupling code ALOHA (Hillairet et al. 2010 Nucl. Fusion 50 125010). The flexibility of the power spectrum by changing the phase difference between adjacent modules was validated and ray-tracing / Fokker-Planck simulations can reproduce the experimental features. The achievable power handling is as high as 25 MW m-2, although with a shot pulse length of ~ 10 s. The first experiment successfully demonstrated the coupling performance of a PAM launcher at low density and this launcher construction provides helpful engineering experience for the 4.6 GHz PAM development in the near future on EAST.

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Section: Coupling Characteristicssupporting

confidence: 77%

First experimental results of the PAM LHCD launcher at 2.45 GHz on EAST

Li¹,

Liu²,

Wang³

et al. 2023

Nucl. Fusion

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“…From these experimental results, we conclude that the electron density in front of the LHCD antennas can be depleted under specific initial conditions when the power is ramped up. Following previous work [5,14,15,[18][19][20], we assume that ponderomotives forces acting on the electrons are responsible for this density depletion.…”

Section: Experimental Characterizationmentioning

confidence: 99%

“…In these regimes, optimal coupling conditions have been found where high power is coupled without any operational issues. Under some other conditions, deleterious effects on the coupling are sometimes observed, which results in an increase in the power reflection coefficient (RC) when the LHCD power is ramped up leading occasionally to trips in the output power [4,5]. Therefore, it is important to investigate and understand the possible origin of such non-linear effects in order to avoid their possible deleterious consequences.…”

Section: Introductionmentioning

confidence: 99%

Experimental characterization and modelling of non-linear coupling of the lower hybrid current drive power on Tore Supra

Preynas¹,

Goniche²,

Hillairet³

et al. 2013

Nucl. Fusion

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To achieve steady-state operation on future fusion devices, in particular on ITER, the coupling of the lower hybrid wave must be optimized on a wide range of edge conditions. However, under some specific conditions, deleterious effects on the lower hybrid current drive (LHCD) coupling are sometimes observed on Tore Supra. In this way, dedicated LHCD experiments have been performed using the LHCD system of Tore Supra, composed of two different conceptual designs of launcher: the fully active multi-junction (FAM) and the new passive active multi-junction (PAM) antennas. A non-linear interaction between the electron density and the electric field has been characterized in a thin plasma layer in front of the two LHCD antennas. The resulting dependence of the power reflection coefficient (RC) with the LHCD power is not predicted by the standard linear theory of the LH wave coupling. A theoretical model is suggested to describe the non-linear wave–plasma interaction induced by the ponderomotive effect and implemented in a new full wave LHCD code, PICCOLO-2D (ponderomotive effect in a coupling code of lower hybrid wave-2D). The code self-consistently treats the wave propagation in the antenna vicinity and its interaction with the local edge plasma density. The simulation reproduces very well the occurrence of a non-linear behaviour in the coupling observed in the LHCD experiments. The important differences and trends between the FAM and the PAM antennas, especially a larger increase in RC for the FAM, are also reproduced by the PICCOLO-2D simulation. The working hypothesis of the contribution of the ponderomotive effect in the non-linear observations of LHCD coupling is therefore validated through this comprehensive modelling for the first time on the FAM and PAM antennas on Tore Supra.

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“…The first one is the Fully Active Multi-junction (FAM) launcher [3] and the second one is the Passive Active Multi-junction [4]. The alternation of passive and active waveguides at the mouth of the antenna provides better coupling properties at low edge electron density (around the cut-off density, n c =1.7*10 17 m -3 ) than the FAM antenna (optimum coupling at [2][3]*n c ) [5].…”

Section: Characterization Of the Non-linear Lhcd Couplingmentioning

confidence: 99%

“…In these regimes, optimal coupling conditions have been found where high power is coupled without any operational issues. Under some other conditions, deleterious effects on the coupling are sometimes observed, which results in an increase in the power reflection coefficient (RC) when the LHCD power is ramped up leading occasionally to trips in the output power [2]. Therefore, it is important to investigate and understand the possible origin of such non-linear effects in order to avoid their possible deleterious consequences.…”

Section: Introductionmentioning

confidence: 99%

Experimental characterization and modeling of non-linear coupling of the LHCD power on Tore Supra

Preynas

Goniche²,

Hillairet³

et al. 2014

AIP Conference Proceedings

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To achieve steady state operation on future tokamaks, in particular on ITER, the unique capability of a LHCD system to efficiently drive off-axis non-inductive current is needed. In this context, it is of prime importance to study and master the coupling of LH wave to the core plasma at high power density (tens of MW/m 2 ). In some specific conditions, deleterious effects on the LHCD coupling are sometimes observed on Tore Supra. At high power the waves may modify the edge parameters that change the wave coupling properties in a non-linear manner. In this way, dedicated LHCD experiments have been performed using the LHCD system of Tore Supra, composed of two different conceptual designs of launcher: the Fully Active Multijunction (FAM) and the new Passive Active Multijunction (PAM) antennas. A nonlinear interaction between the electron density and the electric field has been characterized in a thin plasma layer in front of the two LHCD antennas. The resulting dependence of the power reflection coefficient with the LHCD power, leading occasionally to trips in the output power, is not predicted by the standard linear theory of the LH wave coupling. Therefore, it is important to investigate and understand the possible origin of such non-linear effects in order to avoid their possible deleterious consequences. The PICCOLO-2D code, which self-consistently treats the wave propagation in the antenna vicinity and its interaction with the local edge plasma density, is used to simulate Tore Supra discharges. The simulation reproduces very well the occurrence of a non-linear behavior in the coupling observed in the LHCD experiments. The important differences and trends between the FAM and the PAM antennas, especially a larger increase in RC for the FAM, are also reproduced by the PICCOLO-2D simulation. The working hypothesis of the contribution of the ponderomotive effect in the non-linear observations of LHCD coupling is therefore validated through this comprehensive modeling for the first time on the FAM and PAM antennas on Tore Supra.

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Experimental Investigation of Nonlinear Coupling of Lower Hybrid Waves on Tore Supra

Cited by 4 publications

References 20 publications

First experimental results of the PAM LHCD launcher at 2.45 GHz on EAST

First experimental results of the PAM LHCD launcher at 2.45 GHz on EAST

Experimental characterization and modelling of non-linear coupling of the lower hybrid current drive power on Tore Supra

Experimental characterization and modeling of non-linear coupling of the LHCD power on Tore Supra

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